25.1 The Nature of EnergyEnergy – the ability to do work or cause a change.work is the transfer of energySI unit for energy is the same as the SI unit for work – JouleTwo main types of energy: Kinetic and PotentialKinetic Energy: the energy of motionPotential Energy: Energy stored for use at a later time
3Calculating Kinetic Energy Kinetic Energy: the energy of motionThe amount of kinetic energy depends on the objects mass and velocityEnergy is transferred during workThe more work one does on an object…The more energy one imparts on the objectKinetic energy = Mass x Velocity22When mass is doubled; Kinetic Energy is doubledWhen velocity is doubled; Kinetic Energy is quadrupled!!
4What’s the Kinetic Energy? What is the Kinetic Energy (in Joules) of an object with a mass of 10 kg and a velocity of 10 m/s?When mass is doubled; Kinetic Energy is doubledWhen velocity is doubled; Kinetic Energy is quadrupled!!
5Potential Energy: Energy stored for use at a later time 2 Types: Elastic Potential Energy:Energy stored in springs, bow and arrow, stretched elastic or rubber bands.Associated w/ objects that can be stretched or compressed.Gravitational Potential Energy:Height and weight dependant (notice its weight, NOT mass!)GPE = work done to lift and object to a heightGPE = Weight x Height (remember that weight = mass x 9.8 m/s2)GPE = mass x 9.8 m/s2 x HeightGPE = 100 N x 300 m = 30,000 Nm = 30,000 Joules
6Different Forms of Energy 6 different types:MechanicalThermal EnergyChemical EnergyElectrical EnergyElectromagnetic EnergyNuclear Energy
7Mechanical Energyassociated w/ the motion (kinetic) or position of an object (potential)Kinetic Energy exists whenever an object which has mass is in motion with some velocity. Everything you see moving about has kinetic energy.Potential Energy exists whenever an object which has mass has a position within a force field. The most everyday example of this is the position of objects in the earth's gravitational field.GPE = Weight x Height
8Thermal Energyassociated w/ the total energy of the particles (atoms and molecules) in an object. As thermal energy increases, the particles increase in speed and the thermal energy (temperature) of the object increases.
9Chemical Energythe energy stored in chemical bonds. The potential energy stored in compounds.
11Electromagnetic energy Travels in waves, associated w/ light, infrared, ultraviolet, microwaves, x-rays, etcLonger wavelength yields low frequency & low energyShorter wavelength yield high frequency & high energy
12Nuclear Energy Associated w/ the fusion or fission of nuclear atoms. The fusion of hydrogen into helium fuels the power of the sun
135.2 Energy Conversion and Conservation Most forms of energy can be converted from one type to another.Law of the Conservation of Energy - states that energy cannot be created or destroyed. It simply changes from one form into anotherEinstein’s theory of Relativity - E = mc2a small amount of mass can be changed directly into a tremendous amount of energyE = the energy producedm = the mass being convertedc = the speed of light (186,000 miles/second)
15Section 5.4 Power Power: the rate at which work is done Power = work / time and since:Work = force x distance….Power = Force x DistanceTimeSI Unit for Power is the Watt1 Watt = 1Joule / 1 SecondHorsepower : An American unit of powerThe amount of work a horse does when it lifts33,000 pounds of coal to a height of 1 foot in 1 minute.1 horsepower = 746 wattsJames WattABSame amount of work was done; however there was more power in lifter B since his took less time
16Power ProblemsW = F x DP = F x D / T P = 35 N x 10 m / 5 sec P = 350 J / 5 sec = 70 J/sec P = 70 WattsW = P x T convert 1 hour into seconds: 1 hour 60 min x 60 sec1 hr minWork = 60 watts x 3600 sec = 216,000 Joules= 216 Kilojoules